Mycology — MCQs

Mycology Indian Medical PG Practice Questions and MCQs

Question 171: A patient presented with a swelling in his right foot with multiple discharging sinuses that contained brown granules. The lesion did not respond to antibiotic medications. Which of the following is the causative agent?

A. Sporothrix
B. Actinomadura
C. Madurella mycetomatis (Correct Answer)
D. Nocardia

Explanation: ### Explanation The clinical presentation of a swelling on the foot with multiple discharging sinuses is the classic triad of **Mycetoma** (Madura foot). The presence of **brown/black granules** and the lack of response to antibiotics strongly suggest a fungal etiology (**Eumycetoma**) rather than a bacterial one (**Actinomycetoma**). **1. Why Madurella mycetomatis is correct:** * **Madurella mycetomatis** is the most common cause of Eumycetoma worldwide. * It characteristically produces **black or dark brown granules** (sclerotia) composed of fungal hyphae. * Since it is a fungus, it does not respond to standard antibacterial therapy, requiring long-term antifungals (like Itraconazole) and often surgical debridement. **2. Why the other options are incorrect:** * **Actinomadura (B) and Nocardia (D):** These are causes of **Actinomycetoma** (bacterial). While they also cause discharging sinuses, they typically produce white, yellow, or red granules. Crucially, as bacteria, they *would* respond to antibiotics (e.g., the Welsh regimen/Cotrimoxazole). * **Sporothrix (A):** Causes Sporotrichosis (Rose gardener’s disease). It typically presents as a linear chain of nodules along lymphatic drainage (lymphocutaneous) and does not typically present with a tumefaction of the foot with discharging granules. **High-Yield Clinical Pearls for NEET-PG:** * **Granule Color Clue:** * **Black/Brown:** *Madurella mycetomatis*, *Exophiala*. * **Yellow/White:** *Nocardia*, *Actinomadura madurae*. * **Red:** *Actinomadura pelletieri*. * **Diagnosis:** KOH mount of granules shows septate fungal hyphae in Eumycetoma, whereas Gram stain shows thin, branching filaments in Actinomycetoma. * **Radiology:** The "Dot-in-circle" sign on MRI is a pathognomonic feature of Mycetoma.

Question 172: Which of the following statements is true regarding Cryptococcus neoformans?

A. The capsule excludes India ink particles.
B. It is common in immunocompromised patients.
C. Anti-capsular antibodies prevent recurrence. (Correct Answer)
D. A strongly positive mucicarmine stain of the organism in tissue is useful.

Explanation: ### Explanation **Correct Option: C. Anti-capsular antibodies prevent recurrence.** In *Cryptococcus neoformans* infections, the polysaccharide capsule is the primary virulence factor. While the cell-mediated immune (CMI) response is crucial for clearing the primary infection, the development of specific **anti-capsular antibodies** plays a vital role in opsonization and long-term immunity. These antibodies enhance phagocytosis and are essential in preventing the reactivation or recurrence of the fungus, especially in patients with waning CMI. **Analysis of Incorrect Options:** * **A. The capsule excludes India ink particles:** This statement is actually **true** (making the question technically flawed if multiple options are correct, but in a "choose the best" scenario, C is often highlighted in specific academic contexts regarding immunity). India ink is a negative stain; the large polysaccharide capsule does not take up the ink, creating a clear halo against a dark background. * **B. It is common in immunocompromised patients:** This is also a **true** statement. *C. neoformans* is a defining opportunistic infection in HIV/AIDS patients (CD4 <100). * **D. Mucicarmine stain is useful:** This is also **true**. Mayer’s mucicarmine specifically stains the polysaccharide capsule bright red, which is a diagnostic hallmark in tissue sections. *Note: In many standard medical exams, A, B, and D are well-known facts. If Option C is designated as the "correct" answer in your specific key, it emphasizes the immunological mechanism of long-term protection.* **High-Yield NEET-PG Pearls:** * **Source:** Found in soil enriched with **pigeon droppings**. * **Diagnosis:** **India Ink** (Negative staining), **Latex Agglutination** (detects capsular antigen CrAg—more sensitive than ink), and **Bird Seed Agar** (Niger seed agar) which shows brownish colonies due to phenoloxidase activity. * **Treatment:** Induction with **Amphotericin B + Flucytosine**, followed by maintenance with Fluconazole. * **Pathology:** Causes "Soap bubble" lesions in the brain basal ganglia.

Question 173: A diabetic patient presents with bloody nasal discharge, orbital swelling, and pain. The culture of periorbital pus shows branching septate hyphae. Which of the following is the most probable organism involved?

A. Mucor
B. Candida
C. Aspergillus (Correct Answer)
D. Rhizopus

Explanation: ### Explanation The clinical presentation of a diabetic patient with bloody nasal discharge and orbital swelling strongly suggests **Rhinocerebral Mycosis**. While both *Mucorales* and *Aspergillus* can cause this syndrome, the definitive diagnostic feature in this question is the **morphology of the hyphae**. **1. Why Aspergillus is Correct:** * **Morphology:** *Aspergillus* species are characterized by **narrow, septate hyphae** that exhibit **dichotomous branching at acute angles (approximately 45°)**. * **Clinical Context:** In immunocompromised or diabetic patients, *Aspergillus* can cause invasive rhinosinusitis, leading to tissue necrosis and orbital extension. **2. Why the Other Options are Incorrect:** * **Mucor and Rhizopus (Options A & D):** These belong to the order *Mucorales*. While they are the most common causes of rhinocerebral mucormycosis in diabetics (often associated with ketoacidosis), their morphology is distinct: they show **broad, aseptate (or sparsely septate) hyphae** with **right-angle (90°) branching**. * **Candida (Option B):** *Candida* typically presents as budding yeast cells and **pseudohyphae** (sausage-like constrictions). It does not typically cause invasive, angioinvasive rhinocerebral disease with branching septate hyphae. ### NEET-PG High-Yield Pearls: * **Aspergillus:** Septate hyphae + Acute angle (45°) branching. Think "A" for **A**spergillus and **A**cute angle. * **Mucor/Rhizopus:** Aseptate hyphae + Right angle (90°) branching. Look for "Ribbon-like" appearance. * **Silver Stains:** Both organisms are best visualized using GMS (Gomori Methenamine Silver) or PAS stains. * **Vascular Invasion:** Both *Aspergillus* and *Mucor* are angioinvasive, leading to the characteristic black eschar and tissue necrosis seen clinically.

Question 174: Which of the following is the best stain for fungus?

A. Muciramine
B. Methenamine silver (Correct Answer)
C. Alcian blue
D. Hematoxylin and eosin

Explanation: **Explanation:** The correct answer is **Methenamine silver (Gomori Methenamine Silver or GMS)**. **1. Why Methenamine Silver is the Correct Answer:** GMS is considered the "gold standard" and the most sensitive stain for the routine detection of fungal elements in tissue sections. The underlying principle involves the oxidation of carbohydrates (polysaccharides) in the fungal cell wall by chromic acid to form aldehydes. These aldehydes then reduce the silver nitrate in the methenamine silver solution to metallic silver, staining the fungi **black** against a pale green background. It provides excellent contrast, making even sparse or degenerated fungal hyphae clearly visible. **2. Analysis of Incorrect Options:** * **Mucicarmine (Option A):** This is a specialized stain used primarily to identify **Cryptococcus neoformans**. It stains the polysaccharide capsule of the fungus bright red/pink. It is not a general stain for all fungi. * **Alcian blue (Option B):** This stain is used to detect acidic mucopolysaccharides. While it can highlight the capsule of Cryptococcus, it is more commonly used in pathology to identify mucin-producing tumors or connective tissue disorders. * **Hematoxylin and Eosin (Option D):** H&E is the standard tissue stain. While some fungi (like Aspergillus) may be visible, many are poorly stained or remain transparent, making them easy to miss. **3. Clinical Pearls for NEET-PG:** * **PAS (Periodic Acid-Schiff):** Another excellent fungal stain; it stains fungal walls **magenta/bright pink**. * **Calcofluor White:** A fluorescent stain that binds to chitin; it is the fastest method for direct microscopic examination (requires a fluorescent microscope). * **India Ink:** Used specifically for the negative staining of *Cryptococcus* in CSF. * **Masson-Fontana:** Used to detect melanin in the cell walls of dematiaceous (pigmented) fungi.

Question 175: Which of the following is true regarding microsporidia?

A. It is a fungus
B. It is a protozoan (Correct Answer)
C. It is a bacterium
D. All of the above

Explanation: **Explanation:** Microsporidia are a group of **obligate intracellular parasites** that have historically been the subject of taxonomic debate. For the purpose of medical examinations like NEET-PG, they are traditionally classified and studied under **Protozoology** (Phylum Microspora). **1. Why Option B is Correct:** Microsporidia were long classified as protozoa because they are unicellular, lack mitochondria (mitosomes instead), and possess a unique, complex infection mechanism involving a **polar filament** (or polar tube) to inject sporoplasm into host cells. In clinical medicine and traditional microbiology textbooks (like Ananthanarayan), they are grouped with opportunistic protozoan parasites (e.g., *Enterocytozoon bieneusi*), especially in the context of HIV/AIDS. **2. Why Other Options are Incorrect:** * **Option A (Fungus):** While recent molecular phylogenetic studies (rRNA sequencing) suggest Microsporidia are more closely related to **Fungi** (due to chitin in their spore walls and fungal-like alpha/beta-tubulin), they are still clinically categorized as protozoa in most standardized medical curricula. If "Fungi" and "Protozoa" are both options, "Protozoa" remains the conventional answer for medical entrance exams unless the question specifically asks for "recent molecular classification." * **Option C (Bacterium):** Microsporidia are eukaryotes (possessing a nucleus), whereas bacteria are prokaryotes. **Clinical Pearls for NEET-PG:** * **Most common species:** *Enterocytozoon bieneusi* (causes chronic diarrhea in AIDS patients). * **Staining:** They are best visualized using **Modified Trichrome stain** or **Calcofluor White** (chemofluorescent stain that binds to chitin). * **Drug of Choice:** **Albendazole** is effective for most species, but *E. bieneusi* often requires **Fumagillin**. * **Key Feature:** Presence of a **polar filament** is the pathognomonic diagnostic feature.

Question 176: Chromoblastomycosis is caused by which of the following fungi?

A. Fonsecaea pedrosoi (Correct Answer)
B. Alternaria
C. Exophiala jeanselmei
D. All of the above

Explanation: **Explanation:** **Chromoblastomycosis** is a chronic subcutaneous mycosis caused by a group of **dematiaceous (pigmented/dark-walled) fungi**. These fungi are typically introduced into the skin via traumatic inoculation (e.g., a thorn prick) in individuals working outdoors. 1. **Why Fonsecaea pedrosoi is correct:** It is the **most common cause** of chromoblastomycosis worldwide. The hallmark of this disease is the presence of **Sclerotic bodies (Medlar bodies/Copper-penny bodies)** in tissue sections. These are thick-walled, dark brown, multiseptate structures that represent the diagnostic stage. 2. **Why other options are incorrect:** * **Alternaria:** While it is a dematiaceous fungus, it typically causes **Phaeohyphomycosis**, not chromoblastomycosis. In phaeohyphomycosis, the fungus appears as pigmented hyphae in tissue, rather than sclerotic bodies. * **Exophiala jeanselmei:** This is a major cause of **Eumycetoma** and **Phaeohyphomycosis**. It does not produce the characteristic sclerotic bodies required for a diagnosis of chromoblastomycosis. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Characterized by slow-growing, "cauliflower-like" (verrucous) lesions, usually on the lower limbs. * **Causative Agents:** *Fonsecaea pedrosoi* (most common), *Phialophora verrucosa*, and *Cladophialophora carrionii*. * **Diagnosis:** KOH mount or histopathology showing **Sclerotic bodies** (pathognomonic). * **Treatment:** Itraconazole is the drug of choice, often combined with surgical excision or cryotherapy.

Question 177: Which organism produces black-coloured grains in mycetoma?

A. Leptospira (Correct Answer)
B. Nocardia
C. Actinomadura
D. Phaecremonium

Explanation: **Explanation:** Mycetoma is a chronic, granulomatous infection of the subcutaneous tissue characterized by a triad of localized swelling, underlying sinus tracts, and the discharge of **grains**. These grains are microcolonies of the causative organism, and their color is a critical diagnostic clue. **1. Why the Correct Answer is Right:** * **Leptosphaeria senegalensis** (often abbreviated or confused with *Leptospira* in some question banks, though taxonomically distinct) is a classic cause of **Eumycetoma** (fungal origin). It characteristically produces **large, black grains**. The black color is due to the presence of melanin in the fungal hyphae. Other common causes of black-grain mycetoma include *Madurella mycetomatis* and *Exophiala jeanselmei*. **2. Why the Incorrect Options are Wrong:** * **Nocardia:** This is a cause of **Actinomycetoma** (bacterial origin). It typically produces **white, yellow, or cream-colored grains**. These grains are very small (microsiphosous) compared to fungal grains. * **Actinomadura:** *Actinomadura madurae* produces large **white/yellow grains**, while *Actinomadura pelletieri* is famous for producing **red grains**. * **Phaecremonium:** While *Phaeoacremonium* species can cause eumycetoma, they typically produce **white to pale yellow grains**, not the classic black grains associated with *Leptosphaeria* or *Madurella*. **High-Yield Clinical Pearls for NEET-PG:** * **Eumycetoma (Fungal):** Usually produces **Black** or **White** grains. Hyphae are thick (>15μm). * **Actinomycetoma (Bacterial):** Usually produces **White, Yellow, or Red** grains. Filaments are thin (<1μm). * **Red Grains:** Pathognomonic for *Actinomadura pelletieri*. * **Yellow Grains:** Commonly *Streptomyces somaliensis*. * **Diagnosis:** Grains should be examined with 10% KOH and Gram stain. Culture on Sabouraud Dextrose Agar (SDA) is the gold standard for eumycetoma.

Question 178: Sulphur granules are composed of?

A. Fungal filaments (Correct Answer)
B. Leukocytes
C. Erythrocytes
D. Keratinocytes

Explanation: **Explanation:** **Sulphur granules** are characteristic macroscopic structures found in the pus of patients with **Actinomycosis** (caused by *Actinomyces israelii*) and certain fungal infections like **Mycetoma** (Madura foot). 1. **Why the correct answer is right:** Despite the name, sulphur granules contain no actual sulphur. They are organized micro-colonies of the causative organism. In the context of fungal mycetoma (Eumycetoma), these granules are composed of a dense, tangled mass of **fungal filaments** (hyphae) cemented together by a proteinaceous matrix. In Actinomycosis (a bacterial infection that mimics fungi), they consist of branching bacterial filaments. Under a microscope, these granules often show a "sunburst" appearance due to peripheral clubbing (Splendore-Hoeppli phenomenon). 2. **Why the incorrect options are wrong:** * **Leukocytes:** While pus contains neutrophils and other leukocytes, they form the inflammatory response *around* the granule, not the structural core of the granule itself. * **Erythrocytes:** Red blood cells are not a structural component of these infectious colonies. * **Keratinocytes:** These are skin cells. While mycetoma involves the skin and subcutaneous tissue, keratinocytes do not constitute the granule. **High-Yield Clinical Pearls for NEET-PG:** * **Actinomyces israelii:** Gram-positive, non-acid-fast, anaerobic branching bacilli. Most common cause of "lumpy jaw." * **Eumycetoma:** Caused by fungi (e.g., *Madurella mycetomatis*); granules are usually black or white. * **Actinomycetoma:** Caused by aerobic actinomycetes (e.g., *Nocardia*); granules are usually white, yellow, or red. * **Splendore-Hoeppli Phenomenon:** The deposition of antigen-antibody complexes around the filaments, appearing as eosinophilic radiating processes.

Question 179: Dimorphic fungi grow as molds at which temperature?

A. 37°C
B. 32°C
C. 30°C
D. 25°C (Correct Answer)

Explanation: **Explanation:** Dimorphic fungi are a unique group of fungi that exist in two distinct morphological forms depending on environmental conditions, primarily temperature. This phenomenon is known as **thermal dimorphism**. 1. **Why 25°C is Correct:** At lower temperatures, typically **25°C to 30°C** (ambient/room temperature), dimorphic fungi grow in their **Saprophytic phase** as **molds (mycelial form)**. In this state, they produce hyphae and spores (conidia), which are often the infectious forms found in soil or decaying organic matter. 2. **Analysis of Incorrect Options:** * **37°C (Option A):** This is human body temperature. At 37°C, dimorphic fungi shift to their **Parasitic phase**, growing as **yeasts** (or spherules in the case of *Coccidioides*). This "Yeast at 37°C" rule is a key diagnostic feature. * **32°C & 30°C (Options B & C):** While some growth may occur, 25°C is the standardized laboratory temperature used to define the mold phase in medical mycology. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** "Mold in the Cold, Yeast in the Beast." * **Key Dimorphic Fungi:** *Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides immitis, Paracoccidioides brasiliensis,* and *Sporothrix schenckii*. * **Exception:** *Talaromyces (Penicillium) marneffei* is the only dimorphic fungus that produces a red pigment. * **Coccidioides Exception:** Unlike others that turn into yeast, *Coccidioides* forms **spherules** containing endospores in the tissue (37°C). * **Sporothrix:** Often presents as "Rose gardener’s disease" with lymphocutaneous spread.

Question 180: Which of the following is a dimorphic fungus?

A. Rhizopus
B. Sporothrix schenckii (Correct Answer)
C. Tinea versicolor
D. Microsporum

Explanation: **Explanation:** **Dimorphic fungi** are unique organisms that exist in two distinct morphological forms depending on environmental conditions, primarily temperature. The high-yield mnemonic for NEET-PG is: **"Mold in the Cold (25°C), Yeast in the Beast (37°C/Body temperature)."** **Why Sporothrix schenckii is correct:** * *Sporothrix schenckii* is a classic thermally dimorphic fungus. * In the environment (soil/plants) or at 25°C, it grows as a **mold** with septate hyphae and "flower-like" conidia. * Once inoculated into human tissue (37°C), it converts into a **yeast** form, characterized by "cigar-shaped" bodies. **Analysis of Incorrect Options:** * **Rhizopus (Option A):** This is a member of the Zygomycetes family. It is a **monomorphic mold** characterized by broad, non-septate hyphae with right-angle branching. * **Tinea versicolor (Option B):** Caused by *Malassezia furfur*. While it shows both hyphae and yeast cells on skin scrapings ("spaghetti and meatballs" appearance), it is classified as a **dimorphic yeast** (not a true thermal dimorphic fungus) and is primarily a superficial commensal. * **Microsporum (Option D):** This is a **Dermatophyte**. Dermatophytes are monomorphic filamentous fungi (molds) that infect keratinized tissues. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** *Sporothrix* causes "Rose Gardener’s Disease," presenting as a linear chain of nodules along lymphatic drainage (lymphocutaneous sporotrichosis). * **Drug of Choice:** Oral **Itraconazole** is the preferred treatment. Historically, saturated solution of potassium iodide (SSKI) was used. * **Other Dimorphic Fungi:** Remember the "Body Heat Probably Changes Shape" mnemonic: **B**lastomyces, **H**istoplasma, **P**aracoccidioides, **C**occidioides, **S**porothrix, and *Talaromyces (Penicillium) marneffei*.

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Classification of Fungi

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Superficial Mycoses

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Dermatophytes

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Subcutaneous Mycoses

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Candidiasis

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Aspergillosis

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Cryptococcosis

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Zygomycosis

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Endemic Mycoses

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Opportunistic Fungal Infections

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Antifungal Agents

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Laboratory Diagnosis of Fungal Infections

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Mycology — MCQs

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